Regarding Current

VR3 · February 2005

Ok...

If an amp puts out 200 amps of current..

And you have a 15 amp breaker in ur house, will this amp even work?

If the amp has 20 amp fuses, will it even power on?

How come this makes no sense?

bobman1235 · February 2005

Originally posted by Vr3MxStyler2k3
Ok...

If an amp puts out 200 amps of current..

And you have a 15 amp breaker in ur house, will this amp even work?

If the amp has 20 amp fuses, will it even power on?

How come this makes no sense?

The amp probably puts out 200 WATTS. Divided by 110 volts (watts = amps * volts...) is less than 2 amps.

Your entire house probably doesn't have 200 amps available.

Assuming I remember Electronics class correctly, that is

VR3 · February 2005

ummm no

This amp puts out 1000 at 8 ohms

200 amps of current

and consumes up to 3000 watts

steveinaz · February 2005

Are you sure? 200 amps of draw on the circuit?...that's crazy. Something doesn't sound right...

Current (amps)=Power (watts)/Electromotive Force (volts)

n=amps
n=3000/120
n=25

I come up with 25 amps....

steveinaz · February 2005

Remember:

P (power in watts)
I (current in amps)
E (emf in volts)

P=I*E
I=P/E
E=P/I

VR3 · February 2005

Musical Fidelity says it has 200 amps of current

1000 watts into 8 ohms, mono amp

3000 watts maximum consumption

This whole current thing, is complete and utter BS... means squat...

I dunno wth it is they are 'measuring' when it is posted, but I dont get it

organ · February 2005

What amp is this? 200amps is A LOT. Even industrial equipment don't consume that much.

Maurice

VR3 · February 2005

TOTL Mcintosh, TOTL Musical Fidelity, most all of the TOTL amps out there advertise 200 amps of current

steveinaz · February 2005

There's also a big difference between current "draw" and current output. My parasound has 60 ampere "output" capability, but doesn't draw anywhere near that.

VR3 · February 2005

Then what is the point of it???

I mean, what is it that they are measuring and how does this help the amp do what it has to do exactly?

danger boy · February 2005

maybe the amp is capable of doing 200 amps. but that would be way to high. maybe it's more like 20amps instead. and the extra 0 is just dust. LOL

wlrandall · February 2005

Sounds like they're giving the mysterious Instantaneous Current rating like H/K has done for years. If it's true, it would only be for microseconds. That 10 ga. power cord (or whatever size it is) would turn into a freaking heating element right before it evaporated.

At an RMS of 1kW, you're below 10A. I wouldn't worry about it unless the electrical system in you house is whacked.

What are you driving with this beast?

VR3 · February 2005

I dont own this amp

(like 20 grand man)

Was just curious how companies, all of them get amp ratings, when none of it makes sense...

Thanks for all of the responses

shiu · February 2005

Since you did not say the amp draws 200A, you said it puts out (meaning output, not input) 200A, in that case, it can at least make some sense, consider the following:

1. 15A circuit at 120V can supply a 1800W load, but not more.

2. 25A circuit at 120V can supply a 3000W load.

2. 15A at 120V could give you an output of 60A at 30V.

So if the d.c. rail of an amp is at 30V, it can theorectically deliver close to 60A continuously. With some huge capacitors, it is therefore conceivable that the amp can deliver 100A per channel X 2 for a very short duration, into a very low impedance load.

When we talk about current output, we must also specify the voltage level. Yes, we know V=IR, P=VI, or P=I^2(square)R, or P=V^2(square)/R but don't forget for transformers,

Is=Ip*Vp/Vs, so current can get much higher on the low voltage side, depending on the transformer ratio.

Is is the transformer secondary current
Ip is the transformer primary current
Vs is the transformer secondary voltage
Vp is the transformer primary voltage.

For a step down transformer, secondary side means the low voltage side.

dorokusai · February 2005

Shiu mentioned a keyword here, CAPS....have you forgotten what they do aside from they just look big?

This is an internal figure.

VR3 · February 2005

They store the power, no?

I really am ignorant with the workings of electronics...

hamzahsh · February 2005

I have found a really great website:
Checkout!

http://bugclub.org/beginners/math/WattsVoltsAmps.html

HBombToo · February 2005

Originally posted by Vr3MxStyler2k3
Ok...

If an amp puts out 200 amps of current..

And you have a 15 amp breaker in ur house, will this amp even work?

If the amp has 20 amp fuses, will it even power on?

How come this makes no sense?

What amp are you looking at.

+

there is a difference in reserve verse delivery. your asking the right questions there little bro.

twin

VR3 · February 2005

Well the amp I was referenceing to is the Musical Fidelity KSW or w/e (their big mono amp)...

But really, I'm talking about any amp...

B&K advertises 75...
Rotel advertises like 90 or 120, etc etc

I just dont understand what they are advertising...

jdhdiggs · February 2005

Doro and the rest of the caps crowd are right on this Sid.

A grossly simplified explanation: A cap will store the power in the form of voltage from the power supply for times when the "wall" can not provide the power. The caps then provide their power back into the system as needed. The 200Amps would be possible, but only for an extremely short time. Also, you would never run that many amps due to the fact that the voltage on the rails would never get high enough.

V=IR so at 200 Amps and assuming a low speaker resistance of say 2 Ohm, thats 400V! At 8 Ohms, its 1600V!

Most amps i have seen stop at between 70 and 110V on the rails

McLoki · February 2005

My cinepro is rated at 120amp/channel. (6 channel amp) 350watts/channel into 8 ohms (500 watts/channel into 4 ohms).

They recommend it run on 20-30amp circut at 110 volts. They do say the power will actually increase if you can run it on a 20amp 220 volt circut. (not user changeable 110 - 220, I would have to send it in) From what I understand, if you try to run it on a 15 amp breaker you will be resetting the circut alot.

These are all peak figures however. The Torriod (looks like a very heavy donut) inside the amp acts as a large holding tank for the power. The speakers siphen off of it and the wall current acts as pipe to fill it. This allows the speakers to have the power to handle peaks and not blow a circut every time something blows up on screen.

I have asked a local engineer at work how this works and will post again when he gets back to me.

Michael

bknauss · February 2005

Wow, crazy stuff flying around here.

Let's make some sense of it:
1. Caps store voltage. They are nice because in certain situations because if you don't have enough current, the voltage will sag... if you have caps, they keep the voltage rails up longer than if there were no caps.

2. If 200A is coming out of the amp and going into 8 ohms, that means... P=I^2*R... (200)^2*8 = 320kW!!!!!Man, even if its a 7 channel amp.. wow... jeez.... wow. Even if this was a totally inefficient class A design (about 10% efficient), that's still 32kW... the extra lost power would turn into heat and burn your house down.

3. Transformers are not "holding tanks"... you might be mixing them up with caps. Transformers simply change the amount of voltage and current from the input to the output(s) of it, while keeping the same total power in an ideal world. So if you start with 120V and 5A and drop the voltage down to 12V on the output, you'd have 50A on the output.

And finally my years of hell getting my engineering degree seem to pay off

McLoki · February 2005

Originally posted by bknauss
3. Transformers are not "holding tanks"... you might be mixing them up with caps.

Damn, I knew I was going to screw that up. Thanks for the clarification....

This is a section from a review on the amp I am running

With an unGodly toroidal transformer, 120,000 µF of filter capacitance, and ±95 volt rails, it delivers, without straining, 350 watts into 8 Ohms, and 500 watts into 4 Ohms with all six channels operating. There are 1,050 Joules of energy storage just waiting to send those bass drums into your wall studs, courtesy of six bipolar output devices per channel.

from another review:

In fact, through the course of a testing procedure that bordered on the abusive, none of the overload LEDs so much as flickered. But make sure to plug this powerhouse into a 20-amp outlet, or you'll be resetting your circuit breakers on a regular basis.

and yet another:

With all channels driven I could not infer any surplus over the rated 350 watts per channel into 8 ohms below the maximum stated THD of 0.15 percent; in fact, in this case the measured channels all clipped at around 285 watts.

But note that my AC line voltage (a dedicated 20-ampere circuit) sagged a full 5 or 6 volts under the strain, which no doubt explains the shortfall. Besides, in a a real-world setting, the odds that all channels of any multi-channel amp would be driven simultaneously in phase at even a tenth as high a level are quite literally nil. Cinepro's literature recommends 20- to 30-ampere AC service; I must admit that I'm not fully certain precisely how much total power the 3k6 can develop. My studio is wired in heavy-duty domestic fashion, but not like a commercial welding shop! Clearly, the 3k6 could safely exploit more current. My advice is that if you're going to spend three grand on an amplifier, pay an electrician a couple of hundred dollars more to install a dedicated, double-wired, 30- or 40-ampere circuit to supply it.

Anyway - I would say that I am running close to the limit for a home amplifier with my wiring. Then again, the speakers I am running (and the levels I am running them at) are nowhere near the limits of the amp so I should not have any problems.

Michael

John K. · February 2005

First, it might be worthwhile to emphasize a point that was briefly touched on: although the power supply coming out of the wall outlet is nominally 120V AC, that isn't what the amplifier works with and 120V can't be used in power calculations. The transformer, rectifier and filter capacitors in the power supply section of the amplifier lower the voltage, rectify it to DC and briefly store it as clean DC for the actual amplification section to use.

There've been various comments applying Ohm's Law here and a useful chart of that in its various forms is found here . The form most applicable to the specs Sid cited(1,000 watts into 8 ohms) would be that amperage equals the square root of [watts divided by ohms], here square root[1000/8]= 11.2 amps at the rated 1,000 watt power.

Any amplifier sold in the U.S. has to use the standards set by the FTC regs for power rating, notably that it has to measured for a continuous period of at least 5 minutes at the rated power. Claims about "high current" or "instantaneous current" lasting maybe a millionth of a second shouldn't be given much weight.

shiu · February 2005

Well Sid, you obvious got the attention of quite a few E.E. I did my part, and am glad to see many seem to agree.

Basically, it can make sense, as long as you have the following conditions:

1. A dedicated heavy current circuit, 25, 30 or even 60A circuit.
2. Preferably a 220V circuit if the amp can take it.
3. The amp has huge capacitors, say 200,000 microfarads min.
4. You are talking short duration rating, not continuous.
5. The impedance of your speakers is under 1 ohm at certain frequencies.
6. Your have music/movie source material that call for frequencies at which your speaker's impedance will fall to less than 1 ohm, e.g. 50V/0.25 ohm will give you 200 amperes, mono, or 100 amperes per channel stereo=200 amperes total.

It is possible from EE (or physics) stand point but unlikely that it would actually happen in real ife conditions.

TN_Polk_Lover · February 2005

Wow! This is one of the most imformative threads I've read in a long time.

I love this forum.

Regarding Current

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